2019-05-25T13:32:14ZDiscovering topical interactions in text-based cascades using hidden Markov Hawkes processeshttps://repository.iitgn.ac.in/handle/123456789/3913
Discovering topical interactions in text-based cascades using hidden Markov Hawkes processes
Bedathur, Srikanta; Bhattacharya, Indrajit; Choudhari, Jayesh; Dasgupta, Anirban
Social media conversations unfold based on complex interactions between users, topics and time. While recent models have been proposed to capture network strengths between users, users' topical preferences and temporal patterns between posting and response times, interaction patterns between topics has not been studied. We propose the Hidden Markov Hawkes Process (HMHP) that incorporates topical Markov Chains within Hawkes processes to jointly model topical interactions along with user-user and user-topic patterns. We propose a Gibbs sampling algorithm for HMHP that jointly infers the network strengths, diffusion paths, the topics of the posts as well as the topic-topic interactions. We show using experiments on real and semi-synthetic data that HMHP is able to generalize better and recover the network strengths, topics and diffusion paths more accurately than state-of-the-art baselines. More interestingly, HMHP finds insightful interactions between topics in real tweets which no existing model is able to do.
2018-09-01T00:00:00ZGeneric Single Edge Fault Tolerant Exact Distance Oraclehttps://repository.iitgn.ac.in/handle/123456789/3671
Generic Single Edge Fault Tolerant Exact Distance Oracle
Gupta, Manoj; Singh, Aditi
Given an undirected unweighted graph G and a source set S of |S|=? sources, we want to build a data structure which can process the following query {\sc Q}(s,t,e): find the shortest distance from s to t avoiding an edge e, where s?S and t?V. When ?=n, Demetrescu, Thorup, Chowdhury and Ramachandran (SIAM Journal of Computing, 2008) designed an algorithm with O~(n2) space (O~(?) hides poly logn factor.) and O(1) query time. A natural open question is to generalize this result to any number of sources. Recently, Bil{\`o} et. al. (STACS 2018) designed a data-structure of size O~(?1/2n3/2) with the query time of O(n?????) for the above problem. We improve their result by designing a data-structure of size O~(?1/2n3/2) that can answer queries in O~(1) time. In a related problem of finding fault tolerant subgraph, Parter and Peleg (ESA 2013) showed that if detours of the {\em replacement} paths ending at a vertex t are disjoint, then the number of such paths is O(n?????). This eventually gives a bound of O(nn?????)=O(?1/2n3/2) for their problem. {\em Disjointness of detours} is a very crucial property used in the above result. We show a similar result for a subset of replacement path which \textbf{may not} be disjoint. This result is the crux of our paper and may be of independent interest.?
2018-05-01T00:00:00ZSimple dynamic algorithms for Maximal Independent Set and other problemshttps://repository.iitgn.ac.in/handle/123456789/3626
Simple dynamic algorithms for Maximal Independent Set and other problems
Gupta, Manoj; Khan, Shahbaz
2018-04-01T00:00:00ZA new approach to deanonymization of unreachable bitcoin nodeshttps://repository.iitgn.ac.in/handle/123456789/3549
A new approach to deanonymization of unreachable bitcoin nodes
Mastan, Indra Deep; Paul, Souradyuti
Mounting deanonymization attacks on the unreachable Bitcoin nodes -- these nodes do not accept incoming connections -- residing behind the NAT is a challenging task. Such an attack was first given by Biryukov, Khovratovich and Pustogarov based on their observation that a node can be uniquely identified in a single session by their directly-connected neighbouring nodes (ACM CCS'15). However, the BKP15 attack is less effective across multiple sessions. To address this issue, Biryukov and Pustogarov later on devised a new strategy exploiting certain properties of address-cookies (IEEE S&P'15). Unfortunately, the BP15 attack is also rendered ineffective by the present modification to the Bitcoin client.
In this paper, we devise an efficient method to link the sessions of unreachable nodes, even if they connect to the Bitcoin network over the Tor. We achieve this using a new approach based on organizing the block-requests made by the nodes in a Bitcoin session graph. This attack also works against the modified Bitcoin client. We performed experiments on the Bitcoin main network, and were able to link consecutive sessions with a precision of 0.90 and a recall of 0.71. We also provide counter-measures to mitigate the attacks.
2018-03-01T00:00:00Z